Induction of defense-related responses in Cf9 tomato cells by the AVR9 elicitor peptide of cladosporium fulvum is developmentally regulated.

The AVR9 elicitor from the fungal pathogen Cladosporium fulvum induces defense-related responses, including cell death, specifically in tomato (Lycopersicon esculentum Mill.) plants that carry the Cf-9 resistance gene. To study biochemical mechanisms of resistance in detail, suspension cultures of tomato cells that carry the Cf-9 resistance gene were initiated.

Correlation between binding affinity and necrosis-inducing activity of mutant AVR9 peptide elicitors.

The race-specific peptide elicitor AVR9 of the fungus Cladosporium fulvum induces a hypersensitive response only in tomato (Lycopersicon esculentum) plants carrying the complementary resistance gene Cf-9 (MoneyMaker-Cf9). A binding site for AVR9 is present on the plasma membranes of both resistant and susceptible tomato genotypes. We used mutant AVR9 peptides to determine the relationship between elicitor activity of these peptides and their affinity to the binding site in the membranes of tomato.

Molecular and biochemical basis of the interaction between tomato and its fungal pathogen Cladosporium fulvum.

The interaction between the biotrophic fungal pathogen Cladosporium fulvum and tomato complies with the gene-for-gene model. Resistance, expressed as a hypersensitive response (HR) followed by other defence responses, is based on recognition of products of avirulence genes from C. fulvum (race-specific elicitors) by receptors (putative products of resistance genes) in the host plant tomato.

A High-Affinity Binding Site for the AVR9 Peptide Elicitor of Cladosporium fulvum Is Present on Plasma Membranes of Tomato and Other Solanaceous Plants.

The race-specific Cladosporium fulvum peptide elicitor AVR9, which specifically induces a hypersensitive response in tomato genotypes carrying the Cf-9 resistance gene, was labeled with iodine-125 at the N-terminal tyrosine residue and used in binding studies. 125I-AVR9 showed specific, saturable, and reversible binding to plasma membranes isolated from leaves of tomato cultivar Moneymaker without Cf resistance genes (MM-Cf0) or from a near-isogenic genotype with the Cf-9 resistance gene (MM-Cf9). The dissociation constant was found to be 0.

Production of the AVR9 elicitor from the fungal pathogen Cladosporium fulvum in transgenic tobacco and tomato plants.

Three constructs were used to study the expression of the avirulence gene Avr9 from the fungal tomato pathogen Cladosporium fulvum in plants. They include pAVIR1, pAVIR2 and pAVIR21, encoding the wild-type AVR9 protein and two hybrid AVR9 proteins containing the signal sequences of the pathogenesis-related proteins PR-S and PR-1a, respectively. Transgenic tobacco plants obtained with the three constructs showed a normal phenotype and produced AVR9 elicitor with the same specific necrosis-inducing activity as the wild-type AVR9 elicitor produced in planta by isolates of C.